The primary objective of the proposed research is to design, build and test a sway platform to validate the therapeutic exercises widely used by physical therapists for the restoration of function following stroke. The low cost platform will be connected to a home computer through the game port and will act in much the same way as the joy stick which is commonly used to control video games. The principle to be used is that any postural movement by the subject that alters the position of the center of pressure will be detected by the platform and will result in a movement of the on-screen cursor. Software will be written for measuring postural sway in standing, which is a standard test for balance, and for measurement of the accuracy and speed of the postural movements required to move the cursor to a given on-screen target. The system will be tested with groups of healthy young and elderly subjects to determine the suitability of the system for measuring balance and control of posture. The subjects will be tested once per week for six weeks to determine learning effects and to obtain baseline information. The final phase of the project will use the same protocol with hemiplegic patients. In order to determine what postural movements are used by the subjects, both healthy and hemiplegic, to effect a shift in the center of pressure, they will be videotaped in both sagittal and frontal planes simultaneously while being tested on the platform. Postural movements that increase weightbearing through the affected lower limb are the basis of therapeutic exercises used in the gait re-education following stroke, thus the platform could be used for treatment purposes. If the proposed system can be built at low cost it could potentially be use in home exercise programs. The advantages that would accrue from this strategy are that the exercises could be made more enjoyable and challenging and they could be individualized to meet the particular needs of a given patient. It is also possible to have the computer monitor how frequently the exercises are done at home and how well the patient performs them thereby providing the therapist with an accurate record with which to assess progress as well as compliance. Apart from the application to the investigation of the restoration of function in hemiplegia the platform could be used to investigate physical therapy treatment techniques in improving balance, weightbearing symmetry, control of postural movements and gait in a number of clinical conditions such as Parkinsons' Disease, lower limb amputees and balance disorders. The feature of the system which allows a subject to control video games on the computer make it particularly attractive to the treatment of balance disorders in children. The potential for future research using the proposed platform is great.